Class: Kafka::FetchOperation

Inherits:
Object
  • Object
show all
Defined in:
lib/kafka/fetch_operation.rb

Overview

Fetches messages from one or more partitions.

operation = Kafka::FetchOperation.new(
  cluster: cluster,
  logger: logger,
  min_bytes: 1,
  max_wait_time: 10,
)

# These calls will schedule fetches from the specified topics/partitions.
operation.fetch_from_partition("greetings", 42, offset: :latest, max_bytes: 100000)
operation.fetch_from_partition("goodbyes", 13, offset: :latest, max_bytes: 100000)

operation.execute

Instance Method Summary collapse

Constructor Details

#initialize(cluster:, logger:, min_bytes:, max_wait_time:) ⇒ FetchOperation

Returns a new instance of FetchOperation.



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# File 'lib/kafka/fetch_operation.rb', line 19

def initialize(cluster:, logger:, min_bytes:, max_wait_time:)
  @cluster = cluster
  @logger = logger
  @min_bytes = min_bytes
  @max_wait_time = max_wait_time
  @topics = {}
end

Instance Method Details

#execute ⇒ Object 



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# File 'lib/kafka/fetch_operation.rb', line 41

def execute
  @cluster.add_target_topics(@topics.keys)
  @cluster.refresh_metadata_if_necessary!

  topics_by_broker = {}

  @topics.each do |topic, partitions|
    partitions.each do |partition, options|
      broker = @cluster.get_leader(topic, partition)

      topics_by_broker[broker] ||= {}
      topics_by_broker[broker][topic] ||= {}
      topics_by_broker[broker][topic][partition] = options
    end
  end

  topics_by_broker.flat_map {|broker, topics|
    resolve_offsets(broker, topics)

    options = {
      max_wait_time: @max_wait_time * 1000, # Kafka expects ms, not secs
      min_bytes: @min_bytes,
      topics: topics,
    }

    response = broker.fetch_messages(**options)

    response.topics.flat_map {|fetched_topic|
      fetched_topic.partitions.flat_map {|fetched_partition|
        Protocol.handle_error(fetched_partition.error_code)

        fetched_partition.messages.map {|message|
          FetchedMessage.new(
            value: message.value,
            key: message.key,
            topic: fetched_topic.name,
            partition: fetched_partition.partition,
            offset: message.offset,
          )
        }
      }
    }
  }
rescue Kafka::LeaderNotAvailable, Kafka::NotLeaderForPartition
  @cluster.mark_as_stale!

  raise
end

#fetch_from_partition(topic, partition, offset:, max_bytes:) ⇒ Object 



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# File 'lib/kafka/fetch_operation.rb', line 27

def fetch_from_partition(topic, partition, offset:, max_bytes:)
  if offset == :earliest
    offset = -2
  elsif offset == :latest
    offset = -1
  end

  @topics[topic] ||= {}
  @topics[topic][partition] = {
    fetch_offset: offset,
    max_bytes: max_bytes,
  }
end